Spring lock for electrical contact plugs



A. R. POOL April 23, 1940.

SPRING LOCK FOR ELECTRICAL CONTACT PLUGS Filed March 2'?, 1959 nventor0L @Lam Patented Apr. 23, 1940 PATENT oFFicE SPRING LOCK FCR. ELECTRICALCONTACT PLUGS Austin R. Pool, Wetmore, Kans.

Application March 27, 1939, Serial No. 264,341

2 Claims.

This invention relates to electrical fittings of that type involving'two pairs of conducting strips or straps adapted to be brought intolatwise slideable engagement for the completion of an electric circuit,in which positive means is provided to insure a good electri-calconnection between the members, as well as one in which the members arereliably locked against accidental breaking of the circuit. With devicesof this kind, of ordinary construction, the connection is easily severedby a slight pull on the electric cord of one or both of the parts.

A further object of the invention is to produce a construction of thegeneral character outlined which will maintain its life over a muchlonger' period than the usual plug, since positive locking means isprovided which takes up wear or looseness of the parts.

Another object of the invention is to produce a construction of thegeneral character mentioned which is strong, durable, ei'licient andinexpensive; and in order that it maybe fully understood, reference isto be had to the accompanying drawing, in which:

Figure l. is a central longitudinal section of an electric fittingembodying the invention.

Figure 2 is a section on the line II-II of Figure 1.

Figure 3 is a central cross-section through Figure 4, a boX-typettingembodying the invention.

Figure 4 is a longitudinal section on the line IV-IV of Figure 3.

Figure 5 is a detail perspective of one of the contact elements of thebox-type tting.

The usual fitting which is adapted for threaded engagement with anelectric socket is shown in Figures I and 2, while Figures 3 and 4,illustrate the permanent type which is mounted in a wall 40 box or thelike, not shown. Referring rst to Figures 1 and 2, the fitting comprisesa cylindrical shell member I of non-conducting material, having a closedend 2 and a center stem 3 projecting from said closed end. The closedend of the shell is formed with a pair of parallel openings 4 onopposite sides of the center stern 3; and the end of the stem carries aprojecting rivet 5. Closing the open end of the shell is an externallythreaded metal cap 6, and extending downwardly from the cap insubstantially parallel spaced relation are a pair of conducting metalstrips 1 and 8 having their opposite ends in close proximity to theopenings 4. The two strips are in non-conductive relation, one of thembeing electrically 56 connected tol the threaded cap Ii from which it issupported, and the other being electrically connected to a centercontact 9 forming a washer between an insulation disk Iii and the upsetend of the rivet 5, or the parts can be otherwise assembled. The othermember' of the iitting comprises 5 a cylindrical non-conducting cap IIfrom which conducting wires I2 extend, the ends of said Wires beingelectrically connected to a pair of parallel strips it and i4 projectingfrom said fitting and spaced slightly closer together than the strips 110 and 8 of the tting iirst described. The parts are electricallyconnected by thrusting the strips I3 and I4 of the second member,through the openings @I of the first member, wher'e they make electricalcontact with the strips I and 8 as 15 common inthe art. The aboveconstruction is by way of example, and forms no part per se, of thepresent invention other than to indicate a general type of fitting ofthe character under consideration. n

Heretofore, various means have been adopted in the endeavor to hold thetwo pairs of strips in good electrical Contact, lbut because of thethinness and softness of the metal forming the parts, it has been foundthat they soon become 25 loose to such a point that electrical contactis not only lost, but the second fitting will fr'equently fail tomaintain its position and becomes quickly separated, even by its ownweight.

In order to maintain positive contact and lock the second tting againstmovement except under a strong pull, I mount a casing I6 in the stem 3of the first tting between the strips 'l and 8 and at right anglesthereto, Within the casing I6 I provide positive frictional pressurelocking means for coacting with the strips I3 and I4 of the second orseparable member, to force them apart into positive contact with thestrips 'I and 8 of the first member'. In the present embodiment of theinvention, the casing IB is cylindrical and may be molded in thenon-conducting stem 3 of the member I. Mounted in said casing is aspring I1 which presses in opposite directions against a pair ofnon-conducting balls I8. The balls come into frictional contact withtheir respective proximate strips I3 and I4 and press them outwardlyagainst their companion strips l and 8, and thus maintain the partstightly together and take up wear and hold a good electrical contact. Inthe preferred construction, the `ends of the strips I3 o and I4 havestops to receive the balls to more reliably lock the two fittings inconnected relation.

In the present embodiment of the invention, the

stops are in the form of a pair of openings I9 into which the balls areseated as will be readily u understood. To stiifen the cap 6, and makeits connection with the member I, the former may have an insulationlining 6a to abut the member i, and be provided with openings 6b and 6cfor the accommodation of the strips 1 and 8, and the stem 3 of themember I. The insulating lining, however, is not essential.

In the permanent or Wall box form of construction, 20 is anon-conducting casing provided with a pair of spaced internal chambers2|, each receiving one of a pair of contact strip members 22. The stripmembers 22 each having an external bolt 23 for connection to electricwires (not shown) as common in the art, and the assembly is adapted tobe secured in an outlet box by means of its cross strap support 24. Thecasing 20 is provided with a pair of openings 25 to receive theprojecting strips 26 extending from a second electrical tting orseparable cap member 21 corresponding in all respects to the member 9above described. A pair of frictional ball members 28 are mounted in acasing 29 carried by the central body portion of the casing 20. Theballs 28 are pressed in opposite directions by a spring 3G. Thisconstruction corresponds in operation to that above described, the balls28 pressing the strips 26 into contact with the strips 22.

From the above description, it will be apparent that I have produced aconstruction embodying all of the features of advantage set forth asdesirable; and while I have described the preferredembodiment, it is tobe understood that I reserve the right to all changes Within the spiritof the invention and without the ambit of the prior art.

I claim:

l. An electric contact plug comprising an insulating shell provided withan inner portion of less diameter than the interior wall of the shelland forming spaced chambers of reduced width at one end and terminatingin ilaring mouths, a pair of insulating balls in said inner portion, aspring tending to project said balls into said chambers, a pair of fiatspring contacts occupying said chambers and bowed toward the balls ofthe shell, corresponding ends of the contacts being free for approachingor receding movement, a second hollow fitting communicating with thesaid flaring mouths, and relatively fixed contact strips projecting fromthe second fitting into said spaced chambers through the reduced portionthereof and said flaring mouths and respectively disposed between and incontact with said bowed portions of the contact strips and said balls,the said fixed strips having openings to partially receive the springurged balls to lock the strips against accidental disengagement throughrelative endwise movement.

2. An electric contact plug comprising an insulating shell provided withan inner portion of less diameter than the interior wall of the shelland forming spaced chambers of reduced width at one end and terminatingin flaring mouths, a pair of insulating balls in said inner portion, aspring tending to project said balls into said chambers, a pair of ilatspring contacts occupying said chambers and bowed toward the balls ofthe shell, corresponding ends of the contacts being free for approachingor receding movement, a second hollow tting communicating with the saidflaring mouths, relatively xed contact strips projecting from the secondfitting into said spaced chambers through the reduced portion thereofand said flaring mouths and respectively disposed between and in contactwith said bowed portions of the contact strips and said balls, the saidxecl strips having openings to partially receive the spring urged ballsto lock the strips against accidental disengagement through relativeendwise movement, electric conductors leading from the iixed contactstrips exteriorly of the second fitting, a threaded metal socketreceiving the first-named tting and electrically connected to one of thebowed contact strips, a center contact carried by said rst-named iittingin electric connection with the other bowed contact and insulated fromthe threaded socket.

AUSTIN R. POOL.

